Overview and definition
Squamous odontogenic tumor (SOT) is a rare, benign, locally infiltrative epithelial odontogenic neoplasm composed of islands of well-differentiated squamous epithelium within a mature fibrous connective tissue stroma.[1][2] The tumor is believed to originate from the epithelial cell rests of Malassez in the periodontal ligament or, less commonly, from remnants of the dental lamina.[3][4] SOT is confined to the tooth-bearing regions of the jaws, with a predilection for the anterior maxilla and posterior mandible.[2] The pathogenesis remains uncertain. Radiographically, the hallmark is a triangular or semicircular radiolucency in the alveolar bone associated with the roots of erupted teeth.[4] Conservative surgical excision is curative in most cases, with recurrence occurring in a minority.[1]
Terminology and classification
The WHO Classification of Head and Neck Tumors (5th edition, 2022; updated 2024) classifies SOT as a benign epithelial odontogenic tumor.[1][2] The accepted abbreviation is SOT. The tumor was first described by Pullon et al. in 1975.[3]
- Intraosseous (central) SOT — the predominant form, arising within the jaw bone.[1][5]
- Peripheral (extraosseous) SOT — a rare soft-tissue counterpart arising in the gingival mucoperiosteum.[1][6]
SOT must be distinguished from squamous odontogenic tumor-like proliferations in odontogenic cysts (SOT-LPOC), which are histologically similar intramural squamous epithelial islands occurring within the walls of odontogenic cysts but represent a distinct, non-neoplastic entity with no recurrence potential.[5][7]
Epidemiology
SOT is exceedingly rare. A 2026 systematic review applying WHO 2024 diagnostic criteria identified 65 confirmed lesions (59 intraosseous, 6 peripheral) across the entire published literature.[1] A 2018 pooled analysis identified 110 SOTs (102 central, 8 peripheral) using broader inclusion criteria.[5]
- Age: Wide range; mean age at diagnosis approximately 34 years. Most patients present before age 40.[1][2]
- Sex: Approximately equal distribution, with a slight male predominance noted in the most recent systematic review.[1][2]
- Jaw distribution: No strong predilection for either jaw overall. The anterior maxilla and posterior mandible are the most common specific sites.[1][2]
- Multiplicity: Most lesions are solitary. Rare multifocal cases have been described, sometimes involving both jaws simultaneously.[1][4]
Clinical presentation
SOT typically presents as a slowly growing intraosseous lesion arising within the periodontium.[3][4]
Symptoms and signs
- Often asymptomatic and discovered incidentally on routine radiographs.[2][4]
- When symptomatic, the most common findings are:
Tempo and behavior
- Growth is typically slow and indolent.[2]
- Maxillary lesions tend to behave more aggressively than mandibular lesions, occasionally requiring extensive resection.[4][8]
Peripheral SOT
The peripheral variant presents as a gingival soft-tissue mass without radiographic evidence of bone involvement.[1][6] These lesions follow a benign course without recurrence after excision.[1]
Red flags
Radiographic findings
Location and distribution
SOT arises exclusively in the tooth-bearing (alveolar) regions of the jaws, intimately associated with the roots of erupted, vital teeth.[4][6] The most frequent sites are the anterior maxilla and posterior mandible.[1][2] Lesions are typically solitary; multifocal involvement of one or both jaws is rare.[1][4]
Periphery and shape
The signature radiographic appearance is a triangular or semicircular radiolucency in the alveolar bone, with the base oriented toward the alveolar crest and the apex directed toward the root apices.[1][4] Margins are typically:
- Well-defined with a sclerotic or corticated border[1]
- Occasionally scalloped[1]
- Less commonly, ill-defined in aggressive cases
Internal architecture
- The vast majority of lesions are unilocular radiolucencies.[1][4]
- A multilocular pattern has been reported in a subset of cases and is significantly more common in true SOT than in SOT-like proliferations in odontogenic cysts.[5][6]
- Internal content is uniformly radiolucent without calcified foci on conventional radiographs, although histologic calcification within epithelial islands is occasionally present and may rarely be detectable on volumetric imaging.[6]
Effects on teeth and adjacent structures
- The lesion characteristically involves the lateral root surfaces of erupted teeth, often in the interradicular or periradicular region, mimicking a periodontal defect.[4][9]
- Tooth displacement and widening of the periodontal ligament space may be seen.[1][3]
- Root resorption is uncommon but has been reported.[5]
- Teeth associated with SOT are typically vital.[4]
- Rare cases have been described in association with an unerupted tooth or adjacent to a dental implant.[2][3]
Cortical involvement and growth pattern
- Cortical expansion is common, particularly in larger or maxillary lesions.[3][4]
- Cortical perforation is a recognized feature and is significantly associated with true SOT compared with SOT-LPOC. Volumetric imaging is superior to conventional radiographs for detecting cortical thinning, expansion, and perforation.[5]
- Maxillary lesions may extend into the maxillary sinus or nasal cavity in aggressive cases.[8]
Recognized variants
- Multifocal SOT: Multiple discrete radiolucencies in one or both jaws; rare but clinically significant because of higher recurrence risk.[1][4]
- Aggressive SOT: Larger, ill-defined lesions with cortical destruction, more common in the maxilla.[4][8]
Key radiographic pattern
The combination of a triangular or semicircular alveolar radiolucency associated with the lateral root surfaces of vital erupted teeth, with well-defined sclerotic margins and no internal calcification, is highly suggestive of SOT and should prompt biopsy.[1][4]
Differential diagnosis
The differential for a well-defined alveolar radiolucency associated with the roots of erupted teeth includes common periodontal and odontogenic entities. The triangular or semicircular morphology and lateral root surface location of SOT narrow the differential, but histopathologic confirmation is always required because of significant radiographic overlap.
| Entity | Why it is considered | Best discriminator |
|---|---|---|
| Lateral periodontal cyst | Well-defined unilocular radiolucency between roots of mandibular premolars | SOT shows a triangular configuration with sclerotic margins and may cause tooth mobility; lateral periodontal cyst is typically round or ovoid without tooth mobility[1][4] |
| Odontogenic keratocyst | Unilocular or multilocular radiolucency in the posterior mandible | OKC tends to grow along the medullary cavity with minimal expansion; SOT is confined to the alveolar process with a characteristic triangular shape[1][5] |
| Ameloblastoma (acanthomatous type) | Multilocular radiolucency with cortical expansion in the posterior mandible | Ameloblastoma is typically larger with a soap-bubble or honeycomb pattern, marked expansion, and root resorption; histologic distinction is critical as SOT lacks peripheral palisading and stellate reticulum[2][5][6] |
| Intraosseous squamous cell carcinoma | Ill-defined radiolucency with cortical destruction | Irregular, moth-eaten margins, periosteal reaction, and paresthesia favor carcinoma; SOT shows well-defined sclerotic borders and no cellular atypia[2][6][10] |
The highest-risk diagnostic pitfall is misdiagnosis of SOT as ameloblastoma or squamous cell carcinoma on incisional biopsy, which may lead to unnecessarily aggressive surgery. Careful clinicopathologic correlation — integrating the characteristic alveolar location, triangular radiographic morphology, and bland squamous histology without peripheral palisading — is essential to avoid overtreatment.[2][4]
Histopathology
Diagnostic microscopic features
SOT is composed of variably sized islands, nests, and cords of well-differentiated, cytologically bland squamous epithelium dispersed within a mature fibrous connective tissue stroma.[2][4][6]
- Epithelial islands are uniform without peripheral columnar cell palisading or stellate reticulum — features that distinguish SOT from ameloblastoma.[3][4][5]
- Central microcystic degeneration (vacuolization) within epithelial islands is common and characteristic.[4][5]
- Occasional keratinization may be present but is not prominent.[4]
- Calcification within epithelial islands occurs in some cases.[6]
- Mitoses are infrequent but may be present and are cytologically normal.[5]
- No cellular atypia, distinguishing SOT from intraosseous squamous cell carcinoma.[6]
- Invasion into cancellous bone trabeculae may be seen, reflecting the locally infiltrative nature.[6]
- A peripheral condensation or hyalinization of fibrous stroma around epithelial islands has been described.[3]
Distinction from SOT-like proliferations
SOT-LPOC consists of histologically identical squamous islands arising as intramural budlike extensions from the epithelial lining of odontogenic cysts, most commonly radicular cysts.[7] SOT-LPOC lacks recurrence potential and is considered a reactive or hamartomatous process rather than a true neoplasm.[5][7] Radiologic correlation is decisive: a unilocular cystic lesion favors SOT-LPOC, whereas a multilocular or triangular alveolar radiolucency favors true SOT.[6]
Immunohistochemistry
Immunohistochemical studies have demonstrated expression of Notch signaling pathway components (Notch1, Notch3, Notch4, Jagged1, Delta1) in SOT epithelial cells, suggesting a role in cytodifferentiation, though these markers are not used diagnostically.[2] Immunohistochemistry may assist in excluding ameloblastoma and squamous cell carcinoma in difficult cases.[2]
Management and prognosis
Treatment
- Conservative surgical excision (enucleation or curettage) is the standard treatment for most SOTs and is curative in the majority of cases.[1][2][4]
- Extraction of teeth intimately involved with the tumor is frequently necessary; in over half of reported cases, adjacent teeth were removed.[3]
- Aggressive or recurrent lesions — particularly multifocal or maxillary tumors — may require more extensive resection, including en bloc resection or partial maxillectomy.[2][4][8]
Recurrence
- Recurrence occurs in a minority of intraosseous cases after conservative surgery.[1][5]
- Five recurrences were identified among 110 SOTs in a pooled analysis.[5]
- Recurrence may occur months to years after initial treatment; one reported case recurred twice over a 6-year follow-up period.[3]
- Peripheral SOTs have not been reported to recur.[1]
Prognostic factors
- Maxillary location is associated with more aggressive behavior and a higher likelihood of requiring radical surgery.[4][8]
- Multifocality is associated with early recurrence and may necessitate more aggressive initial management.[4]
- Cortical perforation at presentation is more common in true SOT than in SOT-LPOC and may indicate locally aggressive behavior.[5]
Surveillance
Long-term clinical and radiographic follow-up is recommended given the potential for late recurrence, particularly for maxillary and multifocal lesions.[3][4] No established surveillance protocol exists, but periodic imaging at 6- to 12-month intervals for at least several years after treatment is prudent.